netdev - Re: question about nla_nest

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Message-ID: <20110127172118.GA331@e-circ.dyndns.org>
Date:	Thu, 27 Jan 2011 18:21:18 +0100
From:	Kurt Van Dijck <kurt.van.dijck@....be>
To:	Julia Lawall <julia@...u.dk>
Cc:	hadi@...erus.ca, netdev@...r.kernel.org
Subject: Re: question about nla_nest_cancel

On Thu, Jan 27, 2011 at 06:08:34PM +0100, Julia Lawall wrote:
> 
> I find numerous occurrences of code like the following, in which nest ends 
> up with the value NULL and then nla_nest_cancel is called with nest as the 
> second argument.  But nla_nest_cancel just calls nlmsg_trim with the same 
> second argument, and nlmsg_trim does nothing if its second argument is 
> NULL.  Is there any reason to keep these calls?
I just learned this:
nla_nest_start() adds data to the skb.
nla_nest_end() 'commits' the proper length.
nla_nest_cancel() reverts skb to the state before nla_nest_start(),
as if nothing happened.

Kurt
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